1. Field of the Invention
The present invention relates to a color wheel according to the generic term of claim 1, as well as a picture generation unit according to patent claim 12.
2. Description of the Pertinent Art
Devices of the aforementioned type are used in applications where periodic color changes need to be produced in an optical system in rapid sequence such as in novel picture generation devices or display arrangements. In order to produce such color changes, color filters are inserted into the optical light path in rapid sequence. For this purpose a disc-shaped color wheel is used that is equipped with circularly arranged filter segments on the periphery that form a ring and are rotated around the central axis of the wheel. Through the rotation of the color wheel the filter segments are alternatingly inserted into the optical path and thereby the desired periodic color change is produced (The Eduard Rhein Foundation/Texas Instruments Inc., Digital Micromirror Device DMD). Because the picture generation device must be able to produce a high picture quality, the color changes must be executed very rapidly. This means that the filter segments must be moved through the light beam at very high speed. As a result large forces due to accelerations which are several hundred times larger than the acceleration g due to gravity act on the color wheel and particularly on the sensitive filter segments; for particularly high picture qualities the accelerations can exceed 1000 g. In addition the radial concentricity of the device must be highly accurate in order to achieve a long operational life of the device. Such picture generation devices must also satisfy very high brightness requirements which can only be achieved with powerful light sources. Through these powerful light sources the device is subjected to correspondingly high temperatures of up to 100.degree. C. For these reasons the holding power and color stability of the filter segments must fulfill very demanding requirements. Broad-scale utilization in so-called low-cost display applications is only feasible if it becomes possible to produce the color wheel at very low costs despite the high quality requirements.
A color wheel with circularly arranged filter segments for use in picture generation devices is described in EP 0 615 156 A2. In this device the filter segments are mounted on a glass ring. The disadvantage of this arrangement is that the glass ring is expensive. In addition, precise radial concentricity is difficult to achieve. The glass ring produces additional light loss which impairs the economy of the overall arrangement. In addition color wheel arrangements are known that feature fixing elements such as spokes between the segments, but also these lower the overall transmission values of the color filter rings and limit the economy.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure and are entirely based on the Swiss Priority application No. 1091/96, filed on Apr. 30, 1996.
The purpose of the present invention is to create a device that remedies the disadvantages of the current state of the art. In particular the color wheel shall be able to satisfy the demanding optical and mechanical properties over a long operational life and be economical to manufacture.
This task is solved by the present invention based on the design according to claim 1.